The seasonal variations of ultraviolet radiation result in changes of human serum bone turnover markers

Vitamin D is recognized as the sunshine vitamin playing a vital role in maintenance of skeletal health. Vitamin D status depends on latitude, as vitamin D3 is synthesized in the skin under the influence of UV irradiation from the sun mainly during spring and summer. Biochemical markers of bone turnover can be classified according to the process that underlie in markers of bone formation, [bone ALP, osteocalcin] and markers of bone resorption, [pyridinuim crosslinks, collagen I C- and N-terminal telopeptides (CTX-I and NTX-I)].
   The aim of the present study was 1) to investigate in a sunny Mediterranean country like Greece whether bone turnover, as determined by biochemical markers, varies by season 2) to correlate these changes with the quantity of the Ultraviolet radiation (UV) and 3) to determine the degree and the qualitative characters of this variability.
   The study was conducted for one year. The study group was composed of two separate groups; each group included 30 healthy adults (15 male and 15 female). In the first group, were studied in a prospective longitudinal manner and remained the same throughout the year. In the second group of healthy subjects were studied in a cross sectional manner and recruited randomly in the same last week of each season from healthy individuals coming to donate blood at the Hospital Blood Centre. Serum and urine calcium, phosphate, albumin, bone alkaline phosphatase were determined. Urinary calcium was measured on a 24h urine sample, delivered on the day of the blood sampling. Electrochemiluminescence immunoassay “ECLIA” (Roche) was used for quantitative determination of serum bone markers Osteocalcin, TP1NP, PTH, β-CrossLaps, Vitamin D3 (25-OH). The UV-B irradiation was measured at a ground-based station located in Patras (38.29° N, 21.29° E) of the Greek UV Network by a NILU-UV multi-channel radiometer. NILU-UV multi-channel radiometers provide UV irradiance measurements at five wavelength bands centered at 302, 312, 320, 340 and 380 nm, with full width at half maximum (FWHM) of approximately 10 nm.
   Annually changes of serum bone turnover markers appears early in spring. These changes resulted from expected changes of serum Vit D due to seasonal variation of UV radiation: 1) Seasonal Variation of Bone markers turnover in 30 healthy individuals: UV-B (MJ/m2) Winter 1.459, Spring 4.426, Summer 7.475, Autumn 3.438, (n.s.) TP1NP (ng/mL): 43.31±16.34, 52.19±22.33, 45.76±18.20, 44.75±12.95, Vitamin D3(25-OH) (ng/mL): 28.77±4.77, 31.77±6.80, 42.02±14.75, 30.63±7.29, p<0.001, Osteocalcin (ng/mL): 17.70±7.26, 19.95±6.64, 17.46±5.49, 16.86±4.43, p=0.06, Β-Crosslaps (ng/mL): 0.275±0.167, 0.339±0.186, 0.299±0.138, 0.259±0.129, n.s., PTH (pg/ml): 36.80±13.32, 34.46±12.27, 32.92±13.47, 35.64±13.49, n.s., Serum Calcium (mg/dl): 9.55±0.38, 9.39±0.66, 9.47±0.70, 9.58±0.61, n.s. Bone Alkaline phosphatase (IU/L): 51.84±13.66, 51.68±14.71, 42.80±12.48, 51.20±15.14, p<0.001, respectively. 2) Seasonal Variation of Bone markers turnover in 120 healthy individuals (30 every season selected randomly UV-B (MJ/m2): Winter 1.459, Spring 4.426, Summer 7.475, Autumn 3.438, TP1NP (ng/mL): 36.87±10.88, 44.53±21.00, 36.75±12.93, 38.25±16.76, n.s. Vitamin D3(25-OH) (ng/mL): 21.17±6.27, 29.30±8.20, 31.24±10.47, 25.39±5.42, p<0.001, Osteocalcin (ng/mL): 15.25±4.95, 19.35±6.88, 13.81±3.94, 12.42±5.45, p<0.001, Crosslaps (ng/mL): 0.230±0.130, 0.296±0.201, 0.234±0.141, 0.196±0.088, n.s. PTH (pg/ml): 27.62±11.07, 29.12±12.59, 22.62±6.94, 28.91±10.11,n.s. Serum Calcium (mg/dl): 9.39±0.39, 9.79±0.24, 9.78±0.49, 9.80±0.75, p<0.001, Bone Alkaline phosphatase (IU/L): 44.71±12.11, 46.08±14.16, 33.47±11.88, Autumn(-),p<0.001, respectively.
   Based on bone turnover markers, we conclude that bone formation precedes bone resorption.